Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment, as examples. Semiconductor devices are typically fabricated by sequentially depositing insulating or dielectric layers, conductive layers, and semiconductive layers of material over a semiconductor substrate, and patterning the various material layers using lithography to form circuit components and elements thereon.
The semiconductor industry has experienced rapid growth due to improvements in the integration density of a variety of electronic components (e.g., transistors, diodes, resistors, capacitors, etc.). For the most part, this improvement in integration density has come from shrinking the semiconductor process node. With the increased demand for miniaturization, higher speed, greater bandwidth, lower power consumption, and lower latency, there has grown a need for smaller and more creative packaging techniques for semiconductor dies.
Three-dimensional (3D) integrated circuits and stacked chips or wafers are used to solve some development limitations of two-dimensional integrated circuits. Typically, a three-dimensional integrated circuit is formed by using through-vias in a semiconductor substrate, to provide the stacked chip/wafer packaging structures, such as using the through-vias to connect the chips or wafers. Therefore, the lengths of the metal wires and the impedances of the wires/traces are decreased and the chip area is also reduced, thereby having the advantages of small size, high integration, high efficiency, low power consumption, and low cost.
Before making a three-dimensional stack, different chips or wafers are separately completed by suitable front-end processes (such as the processes for forming active devices, connecting the metal lines, and so on), and then the through-vias and the re-distributed layers (RDLs) are used to complete the stack steps of the back-end processes.